Solar Backfeed Issue

[jaggedben]

My point was about panelboards. In my area the main utility doesn't care and no AHJ has ever asked me to combine all my inverter outputs into one feed. I've installed multiple PV breakers in a panelboard with loads many times. Plans have always been submitted and approved ahead of time.

 

[ggunn]

My point was about panelboards. In my area the main utility doesn't care and no AHJ has ever asked me to combine all my inverter outputs into one feed. I've installed multiple PV breakers in a panelboard with loads many times.

Lucky you.

 

[david]

It's really simple. If you're connecting to a busbar or conductor that has no means which disconnects it from the utility, it's a supply side connection. If not, it's a load side connection. Whether any other connections happen in the same enclosure is irrelevant. Whatever else is connected to the same busbar or conductor is irrelevant.

Each connection is certainly one or the other, but you could have both types in series.

There's no question that the last part is a correct interpretation. Any busbar or conductor that cannot be disconnected from the utility is not subject to any of the rules in 705.12(D). Period. It's not load side of a service disconnecting means. I realize lots of people have wrong ideas about this, or take a while to understand, but that's just because they haven't gone back to the code and carefully read what it clearly says.
Whether the two solar handles count towards the six handle for service disconnects is a more open question. People have argued for many pages on this forum about whether the solar breakers would count as service disconnecting means.
The word 'source' probably needs clarification in this section, but it is not intended to refer to the utility. This section should be be re-written, in my opinion. The intent is that (non-utility) sources don't share the same overcurrent protection with loads.
Also, the section you quote is another one of the load side rules. Breakers or switches connected directly to the service do not have to follow it. But per article 230 all the normal (non 230.82) loads need to be connected to the same (six) service disconnecting handle(s).

It's really simple. If you're connecting to a busbar or conductor that has no means which disconnects it from the utility, it's a supply side connection. If not, it's a load side connection.

There's no question that the last part is a correct interpretation. Any busbar or conductor that cannot be disconnected from the utility is not subject to any of the rules in 705.12(D). Period. It's not load side of a service disconnecting means. I realize lots of people have wrong ideas about this, or take a while to understand, but that's just because they haven't gone back to the code and carefully read what it clearly says.

I sincerely believe you know a lot about PV systems but I went on line and googled load side connection I then googled line side connection. The PV published articles that I researched would agree if you tapped the bus of any service panel and then took those PV (service) conductors to a disconnect you would have a line side connection point.

The published articles that I read on this subject stated that if your connection point is through a breaker attached to the bus in the panel you are a load side connection

The difference I see as relevant to this thread is if the PV connection point was to the main lugs in this main lug panel you would be making a line side connection point. That’s not what is happening in this discussion the connection point is through two 20 amp breakers that make the connection in this panel

I am attaching for you consideration a paragraph from the 28th addition of the McGraw Hill’s National Electrical Code 2014 Handbook (Frederic P. Hartwell, Joseph F. McPartland, Brian J. McPartland)

They make note of making use of a MLO 200 amp rated bus panel for a connection point for PV 40 amp breaker.

If this same application was I applied to this discussion a 60 amp breaker for a 100 amp buss MLO panel with 40 amp of PV connection would work in the same way.

 

[david]

To the original poster

If the feeder between the two panels where removed.

A meter was doubled lugged to supply both the original panel and the Main Lug Only Panel was supplied through a 60 amp main breaker

And the MLO panel was treated as an additional service disconnect in the way that the hand book example indicated of course the neutral bond and grounding electrode conductors would be needed to the MLO panel.

All that would be needed is to move some branch circuits (load)from the original service panel to the MLO service panel

Edit: if i did not make it clear as to why a MLO panel was suggested over a 60 amp service panel it was to make use of a 100 amp rated buss and still have 60 amps of normal disruption with 40 amps of PV connection to this same buss

 

[jaggedben]

... The published articles that I read on this subject stated that if your connection point is through a breaker attached to the bus in the panel you are a load side connection ...

What articles? You didn't cite any.

Load side and supply side of the service disconnecting means has a very plain meaning. It's simply wrong to say that the connection being a breaker attached to a busbar has any bearing on it.

 

[jaggedben]

To the original poster

If the feeder between the two panels where removed.

A meter was doubled lugged to supply both the original panel and the Main Lug Only Panel was supplied through a 60 amp main breaker

If the double lugging could be done in a way that did not violate the listing of the meter socket this could be an option.

There's no reason the MLO panel would need to be supplied through a 60A main breaker.

 

[ggunn]

I sincerely believe you know a lot about PV systems but I went on line and googled load side connection I then googled line side connection. The PV published articles that I researched would agree if you tapped the bus of any service panel and then took those PV (service) conductors to a disconnect you would have a line side connection point.

The published articles that I read on this subject stated that if your connection point is through a breaker attached to the bus in the panel you are a load side connection.

You are misinterpreting the article. The placement of the point of interconnection determines whether it is a load side or a supply side connection, not whether it is a switch or a breaker in a panel. If it is on the utility side of a main disconnecting means (service disconnect) it is a line (supply) side interconnection. If the main panel is MLO (no main breaker) and there is no disconnect between the panel and the transformer supplying power to the service, a backfed PV breaker in that panel is a line (supply) side interconnection and all the load breakers in the panel are service disconnects.

FWIW, an AHJ I encounter a lot does not allow supply side connections through breakers. There must be an external fused disco within 10 feet of the panel.

 

[david]

What articles? You didn't cite any.

Load side and supply side of the service disconnecting means has a very plain meaning. It's simply wrong to say that the connection being a breaker attached to a busbar has any bearing on it.

well this article for one.

http://www.homepower.com/articles/s...g-supply-side-connection-article-705/page/0/1

"(using breakers can result in the panel needing to be oversized, for reasons that will be discussed in part 2 on load-side connections). "

"The requirements of NEC Article 230, “Services,” must be followed. A service-rated fused disconnect—the minimum size is 60 amps per Section 230.79(D)—is typically installed for supply side connections (using breakers can result in the panel needing to be oversized, for reasons that will be discussed in part 2 on load-side connections). The load side of the disconnect is connected to the PV system, and the line side to the utility. If the supply side connection is occurring between the main disconnect and the meter, then the new disconnect will count towards the maximum of six switches or breakers allowed per Section 230.71. However, Section 230.2(A) allows for additional services for parallel power production systems—the new meter and disconnecting means for a buy-all sell-all type interconnection should count as a separate service, but this will depend on the interpretation of the AHJ."

 

[jaggedben]

The article you quote does not say that a breaker can't be used as a supply side connection. It merely fails to discuss the possibility.

At any rate, just because someone publishes an article doesn't mean we ignore the plain meaning of the language in the code, but if you want articles, here's one:
http://solarprofessional.com/articles/design-installation/can-we-land?v=disable_pagination

When a supply side connection is made, as permitted by Article 230.82(6), a minimum of two service disconnects are involved: the existing main disconnect and the new PV service disconnect. Although multiple service disconnects may seem unusual, they are actually very common in the field. Article 230.71(A) addresses this issue, stating that no more than six switches or sets of breakers be required to disconnect a service. Commonly referred to as the "six switch rule" or "six handle rule," it makes supply side connections possible; but it can also be a limitation. A problem can arise when main panels are lug fed instead of having a main breaker. A PV breaker landed in this type of panel is a supply side connection and must be counted as one of the six allowed switches. If this type of panel already contains six breakers, and they often do, measures will need to be taken to enable a Code compliant installation.

Let's not get into the discussion of whether PV counts towards the six handles. It's not at issue here and really isn't as clear in the code.

 

[jaggedben]

FWIW, an AHJ I encounter a lot does not allow supply side connections through breakers. There must be an external fused disco within 10 feet of the panel.

Is that because they want it to be lockable, or for some other reason? Would they allow a breaker as long as they also have the lockable disconnect?

 

[david]

The article you quote does not say that a breaker can't be used as a supply side connection. It merely fails to discuss the possibility.

At any rate, just because someone publishes an article doesn't mean we ignore the plain meaning of the language in the code, but if you want articles, here's one:
http://solarprofessional.com/articles/design-installation/can-we-land?v=disable_pagination

Let's not get into the discussion of whether PV counts towards the six handles. It's not at issue here and really isn't as clear in the code.

The article you quote does not say that a breaker can't be used as a supply side connection. It merely fails to discuss the possibility.

I guess my position on this as an inspector will be the article addresses connections on the line side of the service disconnecting means and addresses connections on the load side of the service disconnecting means.

A main lug panel with more than six breakers to disconnect a facility from a utility service is the service disconnecting means. By definition of a service disconnect.

I’m not going to say it is prohibited; my position would be it is not clearly covered in the article. At this point I would conclude the rules for connecting to the buss (breaker)of a main lug panel are not stated in the code sections given.

We have to fall back on the given definition of what is a service disconnecting means. After we define that, a conclusion must be made in determining if this connection point is even addressed in the code

 

[david]

I guess my position on this as an inspector will be the article addresses connections on the line side of the service disconnecting means and addresses connections on the load side of the service disconnecting means.

A main lug panel with more than six breakers to disconnect a facility from a utility service is the service disconnecting means. By definition of a service disconnect.

I’m not going to say it is prohibited; my position would be it is not clearly covered in the article. At this point I would conclude the rules for connecting to the buss (breaker)of a main lug panel are not stated in the code sections given.

We have to fall back on the given definition of what is a service disconnecting means. After we define that, a conclusion must be made in determining if this connection point is even addressed in the code

A main lug panel with not more than six breakers to disconnect a facility from a utility service is the service disconnecting means. By definition of a service disconnect!

 

[wwhitney]

A main lug panel with not more than six breakers to disconnect a facility from a utility service is the service disconnecting means. By definition of a service disconnect!

Actually it is the breakers that are the servicing disconnecting means, not the main lug panel. Per Article 100:

Disconnecting Means. A device, or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.

Device. A unit of an electrical system that carries or controls electric energy as its principal function.

The breakers are the devices, the buss of the MLO panel is conductors, and the cabinet is just an enclosure. Tapping the buss with other conductors and running them to another enclosure with its own device is the same as adding a breaker onto the buss within the existing enclosure.

Cheers, Wayne

 

[wwhitney]

Tapping the buss with other conductors and running them to another enclosure with its own device is the same as adding a breaker onto the buss within the existing enclosure.

When I say that, I mean in the context of the existing discussion on line side versus load side connection of solar. Obviously they are different in other regards.

Cheers, Wayne

 

[david]

Actually it is the breakers that are the servicing disconnecting means, not the main lug panel. Per Article 100:


The breakers are the devices, the buss of the MLO panel is conductors, and the cabinet is just an enclosure. Tapping the buss with other conductors and running them to another enclosure with its own device is the same as adding a breaker onto the buss within the existing enclosure.

Cheers, Wayne

perhaps but then none of the rules in article 230 for line side are applied, and from all the articles i read discussions as what min size conductor and 60 amp min distribution all get skipped over and the installation in every other aspect looks like a load side connection the only significant difference there is no concern for the buss rating. witch leads you to wonder why all the concern with a load side connection

 

[ggunn]

Is that because they want it to be lockable, or for some other reason? Would they allow a breaker as long as they also have the lockable disconnect?

They prefer a switch over a breaker. As to how they would feel about a switch and a breaker, I dunno; I have never asked them because I wouldn't want to design a system that way. It would be a lot more expensive than just a fusible switch next to the MDP and a tap on the busbars.

Edit: A system I am discussing with my local AHJ will have two discos because the MLO MDP is inside the building and they want an accessible lockable disco. The one on the outside of the building will be unfused and the one inside next to the MDP will be fused. They will not let me land on a breaker in the MDP. That sort of answers your question, I believe.

 

[jaggedben]

perhaps but then none of the rules in article 230 for line side are applied, and from all the articles i read discussions as what min size conductor and 60 amp min distribution all get skipped over and the installation in every other aspect looks like a load side connection the only significant difference there is no concern for the buss rating. witch leads you to wonder why all the concern with a load side connection

If you think about it for a minute you'll realize they are totally different situations.

A service conductor has no overcurrent protection ahead of it. The overcurrent protection, such as it is, is at the service equipment which is downstream of the service conductors. Because of this, the load can never be greater than that overcurrent protection allows. It doesn't matter what you do to add sources on the line side of the overcurrent protection at the service equipment.

Example: 100A normal (load) service disconnect and 100A PV only service disconnect. The service conductors, including any busbars, cannot see more than 100A. The 100A can go in either direction but not at the same time.

By contrast, a load-side panelboard with overcurrent protection ahead of it is allowed to have load breakers within it that exceed that overcurrent protection. If you then add a PV source to the panelboard, it could see more than the amount it's rated for.

Example: 100A panel protected by a 100A breaker on the utility side. 150A of load breakers in the panelboard, plus a 20A PV breaker. The loads could theoretically draw 120A of power on the busbar that is only 100A. This is why the PV breaker is required to be at the opposite end, because that way there is no point on the busbar that would actually see 120A. The 120% rule is pretty conservative because panelboard heating from multiple sources hasn't been studied.

 

[david]

If you think about it for a minute you'll realize they are totally different situations.

A service conductor has no overcurrent protection ahead of it. The overcurrent protection, such as it is, is at the service equipment which is downstream of the service conductors. Because of this, the load can never be greater than that overcurrent protection allows. It doesn't matter what you do to add sources on the line side of the overcurrent protection at the service equipment.

Example: 100A normal (load) service disconnect and 100A PV only service disconnect. The service conductors, including any busbars, cannot see more than 100A. The 100A can go in either direction but not at the same time.

By contrast, a load-side panelboard with overcurrent protection ahead of it is allowed to have load breakers within it that exceed that overcurrent protection. If you then add a PV source to the panelboard, it could see more than the amount it's rated for.

Example: 100A panel protected by a 100A breaker on the utility side. 150A of load breakers in the panelboard, plus a 20A PV breaker. The loads could theoretically draw 120A of power on the busbar that is only 100A. This is why the PV breaker is required to be at the opposite end, because that way there is no point on the busbar that would actually see 120A. The 120% rule is pretty conservative because panelboard heating from multiple sources hasn't been studied.

i get that, my comments have been in relationship to a main lug only panel with the PV breakers within that distribution panel. In this thread you currently have a 100 amp load breaker plus 60 amps of PV source.
Currently with a single 100 amp load breaker as you say the current from the utility comes in and leaves from the top of the bus. and the PV current travels the unused portion of the buss to support the utility supply.

But it is being defined as a line side connection and there are no rules stipulating that the PV source breakers has to be connected at any bus location it could be at the top and there are no rules dictating both the 100 amp utility breaker could not be attached at the bottom of the panel at the opposite end of the main lugs connected to the utility supply.

And without any rules since it is a line side connection another PV source breaker could be added to the buss without control in relationship between the load breaker and the PV source breakers,

Would it not be true that a total of 100 amps of PV source breakers could be supplying this 100 amp buss based on the fact that it is a 100 amp service, line side connection rules? What if there were four 50 amp load breakers added in the main lug panel along with 40 amps of PV source with no regard to bus placement

Edit it seems to me the load side rules should be followed when the PV source connection is tied the same buss as load breakes as in this discussion a main lug only panel

 

[wwhitney]

Would it not be true that a total of 100 amps of PV source breakers could be supplying this 100 amp buss based on the fact that it is a 100 amp service, line side connection rules? What if there were four 50 amp load breakers added in the main lug panel along with 40 amps of PV source with no regard to bus placement

If you have a service MLO panel with only one load breaker, and multiple PV source breakers, then as long as the load breaker is less than the bus rating, and the multiple PV source breakers together are less than the bus rating, the bus can't be overloaded.

If you have a service MLO panel with multiple load breakers, forget PV for a moment. The breakers are allowed to add up to more than the service size/bus rating. The only thing protecting that panel bus and the service conductors from overload is the service size calculation under the NEC. Since that's a fairly conservative calculation, that works fine as long as the rules are followed.

Now if you add PV breakers to such a multiple load breaker MLO service panel, nothing changes with respect to overloading the bus. The bus is stilled protected from overload only by the NEC service size calculation. Adding the PV breakers doesn't create any new set of circumstances under which the panel bus is overloaded for which it wouldn't also have been overloaded without the PV breakers.

In your example, the only way to overload that 100 amp bus is if the load breakers together draw more than 100 amps, and that would overload the bus even if the PV breakers weren't there. In fact, for some configurations of breakers and loads, adding the PV breakers could prevent a bus overload that would otherwise occur. It can't contribute to a bus overload that wouldn't otherwise occur.

Cheers, Wayne

 

[wwhitney]

Let me try putting the above in a different way:

In a service panel with multiple breakers, we accept that there is no single breaker that is protecting the panel bus and rely on the NEC service size calculation to protect it. Adding PV breakers doesn't change that.

In all other panels, we require the bus to be protected by a breaker. Adding a PV source breaker to such a panel could circumvent the bus protection provided by that breaker, so that possibility is regulated by the 120% rule.

At least, that is my understanding of the rules.

Cheers, Wayne